1.   Although chalk is a very pure limestone it is mechanically too weak to allow the development of large underground cavities.

2.   This seasonal storage includes the cavity of the depleted Rough field in the North Sea and underground salt cavities.

3.   At the point of explosion, the nuclear fireball carves out an underground cavity.

4.   During the Cold War, scientists refined techniques for detecting underground cavities.

5.   He hopes to have better luck with the help of a radar-tracking device that can identify underground cavities or metal objects.

6.   But sophisticated electronic scanning gear has located two suspicious underground cavities that will be further investigated.

7.   The retreating water dissolved away the soft rock and formed the underground cavities, some of which stretch for miles.

8.   Yerow said most of the grain sorghum stored in traditional underground cavities in the Baidoa region has been destroyed by the flooding.

9.   According to Harrington, the ultrasound equipment revealed two underground cavities, both covered in thick layers of concrete.

10.   Marimuthu, meanwhile, said that tests conducted with sonar equipment on the premises earlier Thursday pointed to three possible underground cavities below a bedroom and lounge.